1. Field of the Invention
The invention relates to a hot water boiler especially though not exclusively a central heating boiler.
2. Description of the Prior Art
Having regard to the rise in the cost of energy, there has in recent years been a strongly felt need for designs of hot water appliances which provide a higher thermal yield in the water. A customary method for expressing the thermal yield of gas-fired boilers is based on the higher calorific value of the fuel i.e. on the calorific value of the fuel including latent heat. With conventional designs for hot water boilers, it is no simple matter to achieve a thermal yield in the water defined in this way exceeding 80%.
Attempts have been made to improve the thermal yield by improved heat exchange between the fumes or burned gases and the water. U.S. Pat. No. 4,282,833 to Giesen describes a boiler having two juxtaposed and mutually connected hollow castings provided with passages for the water and enclosing a combustion chamber and, above it, a burned gas flue. The flue is connected to two passages which extend downwards on either side of the castings, with ribs being cast at either side of the castings projecting into the downward passages and, preferably, also into the water passages.